The present invention is directed to porous groyne structures and method for their use in reclaiming beach and shoreline areas which are subject to erosion by natural forces and, more specifically, to porous groyne structures which are vertically adjustable during use, thereby allowing the porous material of the groynes to be systematically raised as reclamation progresses from the buildup of silt, sand, shells, grasses and other materials.
Beach and other shoreline erosion, especially in coastal areas, is a major concern to property owners who have residences or establishments which are situated in close proximity to the shoreline. Not only is there a tremendous personal and economic loss caused by damage to, or loss of, real estate, housing and commercial buildings by shoreline or beach erosion, but there is also recreational loss of waterfront property which adversely affects the general public.
To deter coastal erosion in many areas, large seawalls are constructed to prevent high tides from reaching land and property. Such structures are costly and are only practical when population densities make it economically reasonable to construct them. Further, such structures have an adverse effect on the natural appearance of the shoreline and, in many areas, cannot be practically constructed.
Other methods of shoreline reclamation include creating jetties or artificial barriers or reefs which extend from the shoreline. These structures are permanent installations and are generally utilized to prevent sand along coastal areas from washing out to sea by wave action. Like seawalls, however, such structures are costly to construct and maintain and, in some areas, are not appropriate for use due to the shoreline configuration, prevailing currents or tidal activity and the like. Also, such structures create a safety hazard in areas where recreational activity is anticipated.
A further method for reclaiming shoreline areas and preventing further erosion is the placement of off-shore, underwater barriers. Often, large porous structures are placed along a sea floor or riverbed at some distance from the existing shoreline. The structures are provided to break wave, current or tidal action thereby creating a zone of low velocity water flow adjacent a beach or riverbank so that sand, silt and other particulate material will settle out of the water before being conveyed by fluid currents out from the shoreline. Again, such outer barriers are only appropriately used in some locations and are not appropriate for use in many locations and may be objectionable for use in some areas due to the adverse affect on aquatic life.
Other methods which are widely used to reclaim shorelines or beaches are dredging and sand importation. When major dunes along a shoreline are damaged or washed away during heavy storms, it is often necessary to import new dirt and sand to re-establish the dunes to provide a natural barrier to tidal activity. Dredgers are commonly utilized to pump sand from a sea floor or riverbed to build up natural barriers. Such methods of shoreline reclamation, however, are temporary measures at best and do not provide a long-term solution to shoreline erosion. Further, such restoration methods are extremely costly and are not practical in many locations.
In view of the foregoing, there is a need to provide a method and apparatus for economically reclaiming damaged shorelines and beach areas which can be practically used in almost any area without an adverse effect to either land or sea environments. In U.S. Pat. Nos. 1,969,123 and 4,710,056, methods and structures for beach restoration are disclosed which utilize netting for purposes of trapping sand, shells and other particulate matter carried by wave action. Nets are extended outwardly from the shoreline and are left in place until a buildup of sand and other particulate matter is established after which the nets, which may be buried several feet or more in the newly collected material, are withdrawn by winches or other means. The removal of the netting material can adversely affect the restored shoreline by creating trenches or furrows which form natural channels in which water flows away from the shoreline thereby conveying particulate matter back to a body of water.
Other examples of porous shoreline reclamation structures are disclosed in U.S. Pat. Nos. 227,483 to Case, 1,060,357 to Nies, 1,948,639 to Youngberg, 1,646,168 to Pringle, 2,097,342 and 2,341,515 to Reheld, 2,135,337 to Herbert, Jr., 2,662,378 to Schmitt, et al., 3,564,853 to Csiszar, 4,861,193 to Newkirk, 4,118,937 to Mansen, 4,738,563 to Clark, 5,108,222 to Jansson, et al., and 5,255,997 to Bailey, et al.